This invention relates generally to lubrication of universal joint assemblies for vehicular as well as industrial use. More particularly, the invention relates to apparatus for enhancing lubrication of needle bearings positioned between trunnions or journals of a universal joint cross member and cylindrical bearing caps supported on the trunnions.
The typical universal joint assembly includes a cross member having four trunnions extending radially outwardly along two perpendicular axes from a central body of the cross member. The ends of the trunnions are rotatably supported on needle bearings contained in bearing cups supported, in turn, by pairs of lugs of two connecting yokes, each yoke coupling separate shafts in a drivetrain. The central body of the cross member has an internal cavity from which internal lubrication passages extend radially through each of the four trunnions. A grease fitting located on the exterior of the central body of the cross member communicates directly with the internal cavity for suppling lubrication into the four passages. Thus, lubrication grease forced into the internal cavity via the grease fitting must travel through the passages to reach the needle bearings.
After a universal joint has been subjected to rotary motion for a period of time, the temperature of the grease will have risen, and the grease will tend to flow freely as a low viscosity liquid. In a typical driveline, the cross member rotates in a generally vertical plane. Upon stopping the joint, unless checked by valves the liquid grease will drain, from one or two of the bearing cups arrested in upper positions, down through the internal passages of the cross member and into the lower cups. If the joint remains idle for a period of time, the grease will cool and congeal back into solid form. Later, upon initial rotation of the joint, the upper cup or cups which have been emptied of lubrication will be subjected to increased wear until such time that the grease can again become liquid to permit adequate flow-back into the affected cup or cups.
Numerous attempts have been made in the prior art to overcome this problem. For example, check valves have been installed in each of the lubrication passages to enable grease to flow only radially outwardly toward the trunnion ends, but not inwardly. However, many of these devices suffer from inoperative or defective valve apparatus. In some instances the grease may not reach all of the trunnion ends in a uniform manner, particularly where wide variations exist in the amount of force required for the grease to pass through the various check valve devices.
Several attempted solutions have involved the use of "standpipe" devices, wherein one end of a tubular structure extends into the lubrication passage of each trunnion, the other end extending into a reservoir in the trunnion end. The intent is to capture or trap a certain amount of lubrication in the reservoir during idle periods. A major problem in the use of such devices relates to sufficient sealing of the standpipe member in the trunnion lubrication passage under typical tolerance variations, and particularly at elevated temperatures. Typical plastic standpipes have a tendency to soften and become dislodged when heated, wherein such devices become ineffective by permitting liquid grease to flow between the standpipe and lubrication passage.